(a) Field of the Invention:
The present invention relates to a controller used with an automotive rearview mirror using electrochromism to automatically adjust the light reflectivity of the inside rearview mirror surface stepwisely accordingly to the brightness in the surroundings of the car or automobile. b) Related Art Statement:
Heretofore, automotive rearview mirrors have already been proposed of which the mirror surface is made of an electrochromic element and colored by changing the voltage applied to the electrochromic element according to the brightness of the surroundings of the automobile, thereby adjusting the light reflectivity of the mirror surface (the rearview mirror of this type will be referred to as "EC mirror" hereinafter). For example, the Applicant's copending Japanese Utility Model Application No. 60-199295 (filed on Dec. 26, 1985) discloses a controller adapted for use with such EC mirror to reduce, when the photosensor disposed at a part of the mirror housing of the EC mirror of a car is exposed to a strong light from the headlights of a car behind the light reflectivity of the EC mirror so that the driver of the car will not be dazzled by the brightness of the light from the headlights of the car behind. As known from the disclosure in the U.S. Pat. No. 4293194, the electrochromic element is of a multilayer structure in which each of two thin chromic layers is placed between transparent electrodes. The first chromic layer is made of, for example, Ni(OH).sub.2 which becomes blue when oxidized, while the second chromic layer is made of, for example, tungsten oxide WO.sub.3 which is colored when deoxidized due to the oxidation of the first chromic layer.
The EC mirror using the above-mentioned electrochromic element has normally a high reflectivity but this reflectivity is automatically changed to a predetermined low reflectivity when the mirror is exposed to a strong light beam from the headlights of a car behind. However, the dazzle felt by the driver's eyes varies depending upon the intensity of the light from the headlights of the car behind. On the other hand, the low reflectivity of the EC mirror is predetermined, namely, fixed at a certain level, so that it cannot be variously changed according to the extent of dazzle felt by the driver's eyes. Also there is a problem that it is difficult to set an optimum low reflectivity at which the driver will not be dazzled.